Suzuki 2 Strokes

So I rebuilt my master cylinder on the buffalo a month or so ago using a NOS Suzuki complete rebuild kit. Finally was warm enough to run her around today and noticed brake fluid leaking from the cap. Popped open the cap and my brand new diaphragm was mis-shaped, not all that soft and falling apart. Rubber was nice and soft on installation, fluid was new dot 3&4. I've never had this happen before on any of the many many bikes I've owned. Any ideas? Happened to anyone else?

There are 3 pieces. Cap, plastic ring and diaphragm. Are you missing the plastic ring?

Nope it's all there. I've ordered another diaphragm, they're only 8 bucks so no big deal. Just really strange that a seemingly perfectly good, new rubber went to crap so quickly.